1. Field of the Invention
The present invention relates to an image forming apparatus, such as a printing machine, a copying machine, a fax machine or a printer, and more particularly to conveyance of recording media in such an image forming apparatus.
2. Description of the Related Art
As to image forming apparatuses, such as printing machines and copying machines, demand has been raised for high-speed and large-volume printing or duplicating/printing in recent years. To meet such a need, for example, a high-capacity paper feeding unit is required to be provided inside the main body of such an image forming apparatus, or a paper feeding table needs to be attached to a lower part of the main body. As a consequence, the whole size of the apparatus—that is, the total height and width of the apparatus—tends to become large.
In the case of an electrophotographic image forming apparatus, the apparatus includes a toner fixing device for fixing unfixed toner on a recording medium. If this image forming apparatus is a high-speed one as described above, toner needs to be fixed on a great number of recording media per unit time, which necessitates the toner fixing means having increased heat capacity in order to prevent fixation failure. Accordingly, the toner fixing device itself becomes large in size due to being equipped with a large-diameter fixing roller, which in turn leads to an increase in size of the image forming apparatus. In addition, large-capacity toner bottles need to be housed inside the apparatus, and thus especially in the case of a full-color image forming apparatus where three or four color toner bottles are necessary, the total height and width of the image forming apparatus can only increase further due to those toner bottles.
With the increase in size of image forming apparatuses, a problem related to jamming has been further exacerbated. Namely, once jamming of paper or the like occurs in a large-sized image forming apparatus, it is sometimes the case that recording media other than the recording medium having caused the jamming also remain inside the image forming apparatus. In jam processing for eliminating the jamming, it is necessary to remove recording media left at various different locations inside the apparatus, thus requiring a lot of time for the jam processing. As the image forming apparatuses make progress toward higher speed and larger capacity, a larger number of recording media tend to be left inside the apparatuses when jamming occurs. Accordingly, the time required for jam processing severely impairs the image forming productivity of the apparatuses.
Patent Document 1 discloses an image forming apparatus in which, even when multiple sheet misfeeds occur—namely, two or more sheets are delivered stacked one on top of another, an image forming operation is performed by feeding sheets smoothly without stopping the conveyance. Here, by switching the sheet conveyance path, sheets causing the conveyance failure are sent to a sheet holding unit which is a tray inside the apparatus dedicated to such misfed sheets. However, according to the invention of Patent Document 1, the sheet holding unit dedicated to misfed sheets needs to be provided inside the image forming apparatus, thus leading to the problem of the main body of the image forming apparatus further increasing in size.
Patent Document 2 discloses a technology aiming at facilitating jam processing performed when a sheet jam has occurred in a collation apparatus, which is a post-processing apparatus of an image forming apparatus. Here, without stopping the operation of discharging sheets from a sheet processing unit, subsequent sheets after the occurrence of the sheet jam are discharged to a temporary tray provided in a sheet reverse discharge apparatus on an extension of the sheet reverse discharge path. However, according to the image forming apparatus disclosed in Patent Document 2, it is necessary to dispose a reverse discharging unit having the temporary tray in front of the post-processing apparatus, thus not allowing the image forming apparatus alone to have the temporary tray function. Accordingly, the disclosed image forming apparatus has to be structured as a so-called image forming system, which leads to problems of a very large installation area and cost increase.
Patent Document 3 discloses an image forming apparatus in which an image forming operation is continuously performed even when a conveyance failure, such as multiple sheet misfeeds, has occurred. Here, by switching the sheet conveyance path, misfed sheets are discharged to a misfed-sheet discharge tray provided outside the apparatus. However, since another tray is required to be provided outside the apparatus, the image forming apparatus of Patent Document 3 has a large breadth, thus resulting in the problem of a large installation area.
Patent Document 4 discloses a technology in which, when jamming occurs in a post-processing apparatus of an input apparatus, such as an image forming apparatus, subsequent sheets after the occurrence of the sheet jam are discharged to a temporary tray by switching the sheet conveyance path. In the image forming apparatus disclosed in Patent Document 4, the temporary tray is provided on the post-processing apparatus, as in the case of the image forming apparatus of Patent Document 2. Thus, the post-processing apparatus connected to the image forming apparatus is necessary, which leads to problems such as a large installation area and cost increase.
In sum, the inventions suggested in Patent Documents 1-4 improve the operability during error recovery processing and the productivity by providing a tray dedicated to sheets of conveyance failures inside or outside of the image forming apparatus, or inside or outside of the post-processing apparatus. However, as has been described, the whole image forming apparatus or system increases in size because of the dedicated tray, thus leaving the problems of a large installation area and cost increase.
Patent Document 1: Japanese Laid-open Patent Application Publication No. 2003-263076
Patent Document 2: Japanese Laid-open Patent Application Publication No. H09-124208
Patent Document 3: Japanese Laid-open Patent Application Publication No. 2006-96502
Patent Document 4: Japanese Examined Patent Application Publication No. S62-18464